shorthair cat / kitten snores and breathing is heavy

I have a male cream British shorthair cat who is 4 months old. I noticed when he’s sleeping he tends to snore and asked the vet when he was getting his jags and vet couldn't find anything wrong. I’ve the vet checked him over again recently for something else. I've now noticed that he tends to breath heavily sometimes during the day but doesn't seem to be causing him any distress and runs around the house without getting out of breath or tired quickly so looks like he is breathing out. Is this common in the British shorthair cat breeds due to the small faces and being less space for the glands causing a eco when breathing through his nose! My 1 year old blue didn’t seem to have this issue but he was very big for his age at 4 months.

Has any other members with British blues noticed this when your cat was a kitten?